It has long been known that solar energy can be converted to electricity in photovoltaic cells. Although several different types of photovoltaic cells, using a variety of materials, have been proposed, most cells have a similar construction. A cell has a photoactive area typically consisting of one or more semiconductor layers sandwiched between two electrodes. These semiconductor and electrode layers are often in the form of film layers deposited on a rigid base substrate, such as glass. Electricity is generated in a semiconductor layer and is collected at the electrodes. A base substrate and all film layers thereon is generally referred to as a substrate, although substrate is sometimes also used to refer only to the base substrate, such as a glass plate. A substrate may contain more than one photovoltaic cell, and often contains many cells, formed on a common base substrate. A substrate that has been completed with one or more photovoltaic cells and which has means for conducting electricity away from the substrate is often referred to as a module.
A typical process for making photovoltaic modules includes: 1) providing a rigid substrate, 2) placing a conductive film on top of the substrate as a bottom electrode, 3) placing one or more semiconducting layers on top of the bottom electrode, 4) placing a conductive layer on top of the semiconducting layer or layers as the top electrode, 5) separating the photoactive area into a plurality of separate cells and interconnecting the cells in series, 6) providing means for conducting electricity away from the electrodes, and 7) encapsulating the panel to protect the active layers from detrimental effects of exposure to weather during use.
Most of the research work performed in the past has been performed in a laboratory environment and has been focused on improving the efficiency of converting solar energy to electricity. Little attention has been given to developing inexpensive and efficient manufacturing techniques that would be required for large-scale production of photovoltaic devices. Such a commercial manufacturing process must be simple and reliable and must include adequate means for handling waste materials. Also, in the research quest for improved cell efficiency, insufficient attention has been given to producing photovoltaic devices that are inexpensive and that are also reliable over extended periods. Although attaining higher cell efficiencies is desirable and should be pursued, higher cell efficiencies should not come at the expense of reasonable manufacturing costs.
A need exists for inexpensive photovoltaic devices that are reliable and durable. A need also exists for efficient manufacturing techniques suited for industrial applications for production of high efficiency photovoltaic modules in commercial quantities.